The thyroid is a small gland found at the base of the neck, just below the protruding cartilage known as the Adam’s apple. It is classified as an endocrine gland, meaning it secretes hormones directly into the blood. The hormones in circulation are transported to all parts of the body including, but not limited to the heart, bone, liver and skin.

The thyroid produces, stores and releases two main hormones called triiodothyronine (T3) and thyroxine (T4). T3 is made from T4 and is the more active or potent hormone. However, the predominant thyroid hormone in the circulation is T4 and has a longer half-life than T3. The half-life is the amount of time it takes for half of the atoms in the hormone to decay. At a ratio of roughly 20 to 1, T4 exists in greater amounts than T3. Also, T4 is converted to the more active or potent T3 within the cells by enzymes. Overall, these hormones directly regulate the body’s metabolism.

The body’s metabolism is the sum of all chemical reactions that take place inside the cells of the body. In particular, the thyroid hormones affect the rates of the components of metabolism, called catabolism and anabolism. Catabolism describes the process when large substances are broken down into smaller ones. When smaller substances combine to form larger ones, this process is known as anabolism. Both components are aided by the thyroid hormones to convert fats, carbohydrates and proteins from the food we eat into the energy necessary to power all reactions and cellular processes.

The excess or deficiency of thyroid hormones will negatively impact the reactions and cellular processes and is not associated with normal health. There is a wide range of signs and symptoms associated with abnormal thyroid functioning. Interestingly, both thyroid hormone excess and deficiency have been associated with specific hair abnormalities, which we will discuss throughout this article.

The Impact

Thyroid disorders have a high prevalence worldwide and are associated with a wide range of diseases with which they may or may not be the cause. The skin is one of the organs which best displays this wide range of clinical manifestations. Additionally, the skin contains a variety of appendages, including sweat glands, sebaceous glands and hair follicles which are impacted by such disorders too.

Thyroid abnormalities are typically diagnosed by the patient’s history and physical examination in addition to the laboratory analysis of one’s blood. A study from the University of Pittsburgh found that the manual examination of the thyroid in patients with hair loss may identify additional thyroid abnormalities not detected with blood analysis alone. Patients who had abnormal manual exams were sent for ultrasounds. The study showed that close to 80% of patients with an abnormal ultrasound exam surprisingly had normal blood thyroid function tests1.

German researchers concluded in a study that thyroid hormones directly alter human hair follicle functions. They discovered that the hormones prolong the growth, also known as the anagen phase and stimulate the proliferation of the hair matrix cells. This is important since the hair matrix produces the actual hair shaft. Their investigation was the first evidence that the hair follicles are direct targets of thyroid hormones and that they affect the cycle of growth3.

Hyperthyroidism and excess

The hair follicles of individuals with hyperthyroidism are thin and fine in texture and appear fatty. Hair loss or alopecia occurs in approximately 30% of individuals with hyperthyroidism. The impact of excessive thyroid hormone causes a shortening of the hair cycle, specifically a shortened anagen and resting or telogen phase. This results in a shorter final length of the hair due to the shorter growth phase2.

The University of Ottawa Eye Institute presented the case of a 19-year-old woman with right upper eyelid eyelash loss. Thyroid function studies confirmed that she had hyperthyroidism. She continued to lose additional eyelashes and a patch of scalp hair. However, once the hyperthyroidism was treated, the eyelashes and scalp hair regrew4.

Hypothyroidism and deficiency

Individuals with hypothyroidism display hair follicles that are dry, brittle and dull. This is attributed to a lower sebum production from the sebaceous gland associated with the hair follicle. Widespread hair loss occurs in approximately 50% of the patients which apparently results from a shorter anagen phase and slower growth2.

Indian researchers investigated the skin manifestations among individuals living in the Kashmir Valley with hypothyroidism. The most common skin manifestation observed in patients with hypothyroidism was dry skin, followed by diffuse hair loss, altered skin texture, coarse scalp hair and puffy face5.

Other Thyroid disorders and hair

Autoimmune thyroiditis is another type of thyroid disorder. All autoimmune diseases involve the process in which the body interprets its own organ, tissue and cells as foreign and produces special antibodies that target and destroys them. The thyroid gland and its hormones in this case are destroyed. Autoimmune thyroiditis may present as either hyperthyroidism or hypothyroidism.

Turkish researchers found that chronic hives, vitiligo and diffuse alopecia were found to be significantly higher in patients with autoimmune thyroid diseases than in the non-autoimmune group6.

A study conducted in India investigated the link between autoimmune diseases and alopecia Areata. Alopecia Areata is a common autoimmune skin disease which results in the loss of hair on the scalp and elsewhere on the body. Initially, one or more small, round bald patches may appear on the scalp and may progress to the complete loss of hair on the scalp in addition to the entire body. The researchers found that autoimmune thyroid disorders showed the highest frequency of this type of hair loss among other autoimmune diseases. Autoimmune hypothyroidism was found to occur most frequently among thyroid disorders in this study7.

In conclusion, the thyroid gland releases its hormones into the blood where they travel to all parts of the body and affect a multitude of individual cells. T3 is the more active hormone and directly impacts the metabolism of each individual cell. One area that the thyroid hormones affect is the skin and its appendages. The hair follicle growth cycle and the hair’s supporting structures including the sebaceous gland are affected by the thyroid hormones. When an excess or deficiency of thyroid hormones exists, the normal functioning of hair will cease and impairment, loss or both will occur.